I. Field of the Invention
The invention is related to distributed amplifiers and in particular to a two dimensional distributed amplifier having multiple phase shifted outputs.
II. Description of the Prior Art
Distributed amplifiers such as taught by A. C. Beck in U.S. patent are well known in the art. A typical distributed amplifier circuit is shown in FIG. 1. The distributed amplifier circuit has an input terminal 10 which is coupled to a plurality of serially connected microstrip transmission lines 14 through 20 by a capacitor 12. The other end of the serially connected transmission lines is connected to a voltage source V.sub.g through a resistance 22 and to ground through capacitance 24. A plurality of amplifiers 26, 36, 42, and 48 are orthogonally connected to the serially connected microstrip transmission lines. Each amplifier has an input connected to a junction between two adjacent microstrip transmission lines. The output of each amplifier is connected to a second plurality of serially connected microstrip transmission lines 30, 32, 40, 46 and 52 by means of a connecting microstrip transmission line, such as connecting microstrip transmission lines 28, 38, 44 and 50 as shown. One end of the second set of serially connected microstrip transmission lines is connected to a voltage source V.sub.D through a low pass filter 34 and the other end is connected to an output terminal 54.
As is known in the art, the microstrip transmission lines will act as an inductance for high frequency signals, which will phase shift the RF signal received at the input terminal 10. Therefore, for the outputs of the distributed amplifiers 26, 36, 42 and 48 to additively combine it is necessary that they remain in phase with each other. To accomplish this, the phase between the inputs to amplifiers 26 and 36 due to microstrip transmission line must be compensated for by phase shifting the output of amplifier 26 using a corresponding microstrip transmission line 32. In a like manner the output of amplifiers 26 and 36 are shifted by microstrip transmission line 40 to keep them in phase with the output of amplifier 42. The additive combining of the outputs of the amplifiers is continued for as many stages as desired.
This basic distributed amplifier concept has been expanded to a two dimensional distributed amplifier as disclosed by S. G. Haing in his article "2-D Distributed Amp Ups Power, Not Load", Microwaves & R.F., April, 1987, pp. 139-142.
Phase shifters are used to electronically steer an antenna in phased array applications. Millimeter-wave shifters will be required as more systems applications are defined to utilize the advantages of this frequency range. Wide band 180 degree power dividers have wide range applications in microwave monolithic balanced and double balanced mixers, push pull power amplifiers and bi-phase modulators. As a result, a digitally controlled RF phase shifting circuit is desired. In particular, a phase shifting circuit capable of phase shifting an RF signal through a predetermined phase angle or predetermined sets of phase angles.
Disclosed herein is a two dimensional distributed amplifier which is capable of generating output signals phase shifted through predetermined phase angles relative to each other.